The present invention relates to an input circuit for use in an integrated circuit, which is driven by a single, positive power supply and is designed to convert an input signal of a negative voltage to an output signal of a positive voltage. More particularly, the invention relates to an input circuit for use in a general logic circuit comprising a gate array, an ECL (Emitter-Coupled Logic) device, a TTL (Transistor-Transistor Logic) device, and a CMOS (Complementary MOS) device, which require input signals at different power supply levels and generate output signals at different voltage levels.
Generally, an ECL device can operate at high speed, but consumes much power. When the logic device coupled to the output of the ECL device does not need to operate at high speed, a TTL device, a CMOS device, and the like--each consuming little power--are used in combination with the ECL device.
There is known an input circuit for use in an integrated circuit comprising an ECL device, a TTL device, a CMOS device, and the like. This input circuit is integrated circuit MC10125, manufactured by Motorola, Inc. Circuit MC10125 converts an output signal of an ECL device, which first rises from -1.7V to -0.9V and then falls to -1.7V, to a signal required by a TTL device, which first falls from +5.0V to 0V and then rises to +5.0V. This IC is driven by two power supplies, i.e., a +5.0V power supply and a -5.2V power supply. In short, circuit MC10125 converts an ECL-level signal to a TTL-level signal when it is driven by two power supplies.
The known input circuit is disadvantageous in two respects. First, it requires two power supplies, i.e., a positive power supply and a negative power supply. Secondly, the elements forming the input circuit must have a breakdown voltage of at least ten volts, in order to withstand both positive and negative power supply voltages. When this input circuit and other circuits are formed on a single chip, not only the elements of the input circuit, but also those of all other circuits must have the above-noted high breakdown voltage.